The poweradjust will always run independent from all other devices. So you can connect it via USB while you can connect the older aquastream pumps with the external controller to the aquaero.
A third aquastream XT can not be connected to the aquaero because it can only handle two pumps at once. Since the aquastream XT offers MUCH more possibilites only through USB that should be no real problem.
Whatever you connect to your PC: the aquasuite will show it all. 5 aquastream XTs, 3 aquaeros, 2 poweradjust and 20 aquaeros - you will be able to control them
(only an example, you can use hundreds of our devices on one PC if you are crazy enough)